Telephone system



Nov. 8, 1932. J. wlcKs TELEPHONE SYSTEM Filed Dec. 14, 1931 PatentedNov. 8, 1932 UNl'iD STTES PATENT OFFICE JOHN XVCKS, Oli' OAK PARK,LLINOS, ASSIGNOR, BY MESNE ASSIGNMENTS, T0 ASSO- iTE-D ELECTRIC?LABORATORIES, ING., OF CHICAGO, ILLINOS, A CORPORATION OF DELAWARETELEPHONE SYSTEM Application ined December 14, 1931.

The present invention relates to telephone systems in general, but isconcerned moreV vertical and rotary switching mechanism;

u ot trunks connected thereto.

and the main object is the production of new and improved circuitarrangements for enabling the sets oi contacts in the bank of a selectorto be variously apportioned amongst the trunk groups accessible fromsuch selector. 'f

GENERAL Dnsoinrrion ils is well known, the ordinary Strowger switch hasone hundred sets of bank contacts arranged in ten horizontal rows orlevels. vWhen this switch is used as a trunk selector, each level otcontacts is ordinarily indexed by diil'erent digits and has a separategroup The s-elector switches are ordinarily mounted side by side ingroups or shelves, with a permanent multiple between the contact banksof all the switches in a shell?, and with arrangements for multiplingthe banks of a number of shelves togeher and for connecting the bankmultiple with outgoing trunks; as is explained in the Mcllyea Patent No.1,633,118, granted J une 2l, 182?. The number of shelves multipledtogether as regards a given level depends upon the relative amount oftratlic carried by the level in question,

In multi-oiiice telephone systems, the various groups olf trunksaccessible to an otiice selector Otten vary greatly in size amongstthemselves. Although, by using suitable grading, a trunk group can beJformed which is in etre-ct a unitary group, but contains many moretrunks than there are Contact sets allotted to the group in the bank oitany one selector, it is desirable, nevertheless, from the standpoint otsecuring the greatest possible ciiiciency in each individualinstallation, to be able to ii crease and decrease the number ot Contactallotted to a contact group to an extent dictated by the relative sizeand cost-per-trunk ot the trunk groups concerned. To this end, thecircuit arrangement has been modified in order to enable the size of acontactgroup in the bank ot the selector' to be sets Serial No. 580,779.

expanded or contracted at will by including any desired portion of thecontacts in the next higher level in the same trunk group with thecontacts in any given level. W'ith this novel arrangement, any level maybe divided into two parts, each part being indexed by a separate digitand belonging to a different trunk group; one part is indexed by thedigit normally assigned to the preceding, lower level, while the otherpart is indexed by the digit normally assigned to the level in question.

In operation, the improved selector responds to the digit dialled in theusual manner by raising its wipers opposite the desired level of bankcontacts. It the digit dialled indexes a group lying partly in thecorresponding level and partly in the next higher level, the operationensuing at the end of the regular directed movement of the selectordepends upon whether there is an idle trunk available in the selectedlevel or not. It there is an idle trunk available, the Wipers of theselector are automatically rotated in search of this idle trunk in theusual manner. But if there is no idle trunk in the selected level, thewipers of the selector are automatically stepped to the next higherlevel and are there rotated over the contacts in such level to test thecontacts assigned to the digit dialled. Y

It will be understood, of course, that selectors which are operated totake an additional vertical step automatically responsive to anall-trunks-busy condition are not broadly new, such selectors beingknown as vertical hunting selectors. lWhenever such selectors have beenused in the past, however, the number of contacts in a selector bankassigned to a trunk group is always increased in multiples of ten, byassigning two levels to a trunk group instead ot one, or by assigningadditional levels as may be required or desired. When such selectors areused, it is manifest that the ,total number ot' trunk groups accessibleto the selector is reduced by an amount depending directly upon thenumber of levels of contacts taken over for over- {iow work. With theimproved selector herein disclosed, however, the number of trunk cuigroups accessible to a selector need not be reduced so long as no trunkgroup has more than nineteen contact sets allotted thereto, for theadditional contacts allotted to one trunk group are in eect merely takenfrom some other group (which other group is thereby reduced in size),and no" group need be entirely cancelled.

From the foregoing explanation, it will be seen that the improved`selector about to be described in detail is arranged so that great'flexibility is a'orded in apportioning theA available total number ofcontact sets amongst the trunk groups which must be reached from theselector.

. A feature of the improved selector is that two separate test wipersare used, cooperating with separate bank contacts, and that one or theother of these test wipers is connected up during the automatic rotationof the selector, depending upon whether the selector is being rotatedover a level to which it was' raised directly responsive to the diallediinpulses, or being rotated over a level to which.

starting in the next lowervlevel.

.Description drawing Referring now to the drawing, comprising :a singlesheet, which shows by means of the unsual circuit diagrams a suliicientamount of apparatus Vin a telephone'systein embodying the features 'ofthe invention to enable the invention to be understood. More inparticular, the drawing shows the circuits of a selector constructed inaccordance with the invention, which selector is accessible by way ofthe trunk line comprising conductors ll, l2, and 13 and is equipped withtest wipers 3l and 32 and line wipers 33 and 34, which are ar- 'rangedto move over the contacts in bank sections 35, 36, and 37, to whichtrunk linesV such as T and Til are connected.

The selector is provided with line relay 20, release relay `2l, seriesrelay 22, series auxiliary relay 23, discriminating relay 24,v

and switching relay 25. ln addition, the selecv tor is provided with theusual vertical, rotary,

and release magnets 27, 28, vand 26; and it has the oil-normal springcontacts i6, 17, and 18, as well as the overflow contacts ll and l5,

which are operated only in case the wipers mon to the selector shown andother similar '3 selectors) are connected by leads 29 and 30 5' with theoverflow contacts ll'forthe usual and Well understood purposes.

31-34 are driven beyond the last set of bank contacts in a selectedlevel. The dial-tone and busy-tone transformers 9 and l0 (com- Theselector, as illustrated, is of the s0- called battery searching type inthat it hunts for a trunk line having a .battery connection thereon.

The dial tone source is associated with the selector under theassumption that the selector is a rstselector, to which the connectionis extended automatically upon the removal of the receiver and in thewell known manner. It will be understood, of course, that, if thisselector is used as a subsequent selector in the trunking system, thedial tone connection is replaced by a ground connection on the middleoverflow contact spring of group 14.

The selector is also provided with a vertical test wiper 33, which isarranged to make successive contact with the contacts in the Ver--tica-lly disposed row as the movement of the switch responsive todialled impulses progresses.

i The Contact grouping rl`he grouping of the bank contacts will now beexplained.V 35, 36, and 37 indicate three separate bank sections of theselector, sections 35 and 37 each comprising one hundred contact pairsarranged in the customary ten levels (of which only three are shown)While section 36 comprises one hundred contacts similarly arranged.Considering the bank ysections collectively, a contact set includes apair of contacts of section 35, the corresponding contact of section 36,and the correspond- Ving pair of section 37. v y It is assumed that thetruck group to which the digit 1 is assigned is a group of ratherexpensive interoffice trunks, while the trunk groups to which the digits2 and 3, respectively, are .assigned are either small trunk groups orelse are relatively inexpensive ,groups not requiring the eliicienttrunk-use -assigned to group 2; and the last seven contact sets in thethird level have been assigned I2 Number Trunk groups Cligrsset ofcontact sets l1 t0 l0, 21 t0 26 16 27 t0 30, 3l. t0 33 7 34 O 40 7 Inexplanation of the'information given in L30 Lesaele the second column ofthe above table, it may be pointed out that contact set number 11 refersto the first contact set in the first level, and that the succeedingcontact sets inthe first row are designated 12, 13, 14, etc. to theninth set, which is numbered 19, and the tenth set is numbered 10. Thenumbering of the contact sets in the higher levels follows the same lan.

It will be understood, of course, that the above indicated apportionmentof contact sets amongst the three trunk groups is given by way ofexample only and that the relative sizes of the assigned contact setsmay be varied at will. It will be understood, moreover, that the size ofthe third contact set may be increased, if desired, by assigning contactsets of the fourth level to the saine trunk group, following the planused in connection with the first and second trunk groups.

DETAILED DESCRIPTION The invention having been describec generally, adetailed description of the operation of the apparatus shown will now begiven.

Seizure of the selector lt will now be assumed that the selector shownin the drawing is seized over the conductors 11 to 13, in which case aground potential is applied to conductor 11, and the loop from a callingline is extended to talking conductors 12 and 1.3. The application of aground potential to conductor 11 results merely in a momentary flow ofcurrent through the resistance element 19, and in tho guarding of theselector against seizure from other sources.

The closing of the loop from the calling line to conductors 12 and 13results in the operation of line relay 2O through the contacts ofswitching relay 25. Then line relay 2O operates, it opens a point in thecircuit of vertical magnet 27 at its lower armature, and at its upperarmature it closes a circuit for the upper winding of release relay 21in series with the lower windings of relays 22 and 21. More in detail,the circuitclosed at the upper armature of relay 2O is as follows: fromground by way of the upper and lower offnormal springs 18, normallyclosed contacts controlled by the iniier-upper armature of release relay21, upper winding of relay 21, up per armature of relay 20, and thelower windings of relays 22 and 21 to battery. The current-flow throughthis circuit is suiiicient to operate release relay 21, whose upperwinding has a relatively large number of turns, but series relay 22 isnot operated in this circuit because the lower winding of relay 22 hasonly a relatively small number of turns.

The same is true as regards the lower winding of relay 21.

Then relay 21 operates, it opens a point in the circuit of releasemagnet 26 at its lower armature; places a ground potential on releasetrunk conductor 11 at armature 51 so as to maintain conductor 11grounded after the ground potential has been removed at the point ofseizure; supplies ground potential direct-ly to the lower terminal ofits upper winding at its inner-upper armature in substitution for theground potential initially applied through olf-normal contacts 18; andat armature 52 it applies ground potential by way of off-normal contacts18 to the upper winding of series relay 22, thereby closing a circuitthrough the upper winding of relay 22 and the lower winding of relay 21,in which circuit the upper winding of relay 22 is shunted around'theupper winding of relay 21 and the lower winding of relay 22. The closingof this new circuit does not disturb the already-operated relay 21, butit results in the strong magnetization of and the immediate operation ofseries relay 22, as the upper winding of relay 22 comprises a relativelylarge number of turns.

lllhen relay 22 operates, it prepares a new circuit for its own Lipperwinding at its upper armature; opens a point in the connection extendingto vertical test wiper 33 at its lower armature; and at its inner-lowerarmature it closes a circuit for the resistancesliunted,series-auxiliary relay 23. Relay 23A Athereupon operates and prepares anoperating circuit for vertical magnet 27 at its innerlower armature;prepares a test cicuit by way of vertical test wiper 38 at its lowerarmature; and at its upper armature it opens a;

point in the circuit of rotary magnet 28.

From the foregoing explanation, it is seen that, responsive to theoperation of line relay 2O when the selector is seized, relays 21, 22,and 23 operate successively, and that the selecto-r is thereby preparedfor operation in response to the usual manipulation of the callingdevice on the calling line.

Dial tone to the calling substation, thereby giving a characteristicsignal to the calling subscriber to inform him that he may now start todial the desired number.

Dzreetz'oely setting the selector When the first digit of the desirednumber is dialed, line relay 2O is deenergized momentarily a number oftimes depending upon the value of the dialled digit. Each time it ismomentarily deenergized, line relay 2O closes a circuit for verticalmagnet 27 at its lower armature, whereupon vertical magnet 27 isoperated to raise the shaft of the switch, together with the wipersaffixed thereto, one

step. By the operation of vert-ical magnet,-

the wipers are, therefore, raised step by step until they come torestopposite the desired level of bank contacts. As a further result oi eachmomentary deenergiZat-ion of line relay 20, the upper winding of relay21 is placed in a local closed circuit at the normally closed contactscontrolled by the upper armature of relay 20,.and the initial circuitfor the upper winding of relay v21 through the lower windings ofrelays22 and 21vis opened. Since the lower winding of relay 21 has onlya relatively small number of turns therein and cannot remain operated inseries with the upper winding of relay 22, the relay is held operatedbetween successive impulses by virture of the circulatingcurrent owingin the closed circuit including the upper winding of relay 21.

As a result of the mechanism of the selector being moved from its normalposition, olinormal contacts 17 prepare a circuit for rclease magnet 26;oil-normal contacts 1G disconnect resistance element 19 4from conductor11 and prepare a circuit ior rotary magnet 2S; and od normal contacts 18open the initial circuit of the upper winding of series relay 22 inseries with the lower winding of release relay 2l, and close a newcircuit for these two windings as follows: from ground by wa i of theinner-upper armature of relay 21, normally closed contacts controlled bythe upper armature et relay 20, upper armature of relay 22, the normallyopen olf-normal contacts in group 18, armature 52, upper winding ofrelay 22, and the lower winding of release relay 21 to battery. By thisexplanation, it will be seen that the circuit initially establis Ledthrough the upper winding of relay 22 and the low winding of relay 21has been shifted so that it is dependent upon normally open contactscontrolled by relay 20, and is closed, therefore, only while relay 20 isin a deenergized condition.

Each time relay 2O :ce-operates following the delivery of an impulse tovertical magnet 27, it removes the shunt i trom around the winding otrelay 21, whereupon this winding is again included in circuit serieswith the lower windings ot relays 22 and 21. At the same time, with thealtered circuit for the upper winding of relay 22 in series with thelower winding of relay 21, current from the upper winding of relay 21divides and a part of it flows through the upper winding of relay 22 onits way to the lower winding ot relay 21. lV ith relay 2O in an operatedcondition, it will be observed that the lower winding of relay 22 isconnected in shunt ont the upper winding ot the relay, and both windingsare in series with the two windings of relay 21. Under this condition,the current-flow through the windings of relay 22 in series with thewindings of relay 21 is insufiicient to maintain relay 22 operated, butrelay 22- remains operated during the receipt of the remaining' impulsesby virtue of the circulating current flowing through its two windings inseries, the upper Winding acting as the driving coil, shunted by thelow-resistance, low-turn lower winding.

l/Vhen line relay 2O comes to rest in an energized condition at the endsof the series oi impulses, the circulating current through the twowindings of relay 22 in series shortly subsides, permitting relay 22 torestore. Upon,

restoring, relay 22 disconnects itsown upper winding at its upperarmature, so as to prevent the relay from subsequently operating untilthe selector has been released and-again seized it connects up thevertical test wiper 38 atits lower armature; and at its innerlowerarmature it opens the initial'circuit of the shunted lseries auxiliaryrelay 23. Relay 28 remains operated for a slight interval because of thecirculating induced current which flows through its winding in serieswith the shunting resistance element.

The vertical test'cz'rcm't 88 is now resting on a test contactassociatedv with the virst level of bank contacts. As will be pointedout subsequently, this Contact is grounded in case all the trunk linesconnected to the contact sets in the irst level are in use, in whichcasethe wipers of the selector `are automatically given an additionalvertical step to bring them opposite the second level.

Tmmc hunting For the purpose of the present description, it will assumedfirst that at least one ofV the trunk lines accessible from the firstlevel of contacts is idle, in which case no ground potential isVencountered by the vertical test wiper 38, and the automatic verticalstep is not taken. Under this condition, thefalling back of the seriesauxiliary relay 23, which follows closely upon the restoration of relay22, results in the closure of a circuit for rotary magnet 28 to rotatethe wipers over the first level of bank contacts.- The circuit forrotary magnet 28 includes armature 51 of relay 21, oli-normal contacts16, overflow contact-s 15, upperv armature of relay 21, upper armatureoir' relay`28, inner-lower armature of relay 25, and theself-interrupting contacts of magnet 2S.

Trim-,7c seizure The-automatic rotation of the wipers'responsive to thebuzzer-like action of magnet 28 continues until switching relay 25operates, upon an idle trunk being encountered.

Assuming that the first idle trunk line encountered is the trunk T10,extending from the tenth set of bank contacts in the iirst level, theadvance of the wipers continues until this trunk line is reached,whereupon the normally connected test wiper 32 encounters a batterypotential by way of test conductor 34, completing an operating circuitfor the upper winding of switching relay 25 to ground at armature 51.Upon operating, relay 25 opens the circuit of rotary magnet 28 at itsinner-lower armature (thereby terminating the rotary movement), at thesame time completing a locking circuit for its lower winding in serieswith rotary magnet 28. Rotary magnet 28 does not operate in series withthe lower winding of relay 25 on account of the high resistance of thiswinding. Switching relay 25 also opens a point in the circuit of releasemagnet 26 at armature 53; connects the now-grounded incomingrelease-trunk conductor 11 directly with the test wiper 32 at its upperarmature, thereby shunting its upper Winding; and at its two lowermostarmatures it disconnects the incoming conductors 12 and 13 from thewindings of the line relay 20 and extends them by way of wipers 33 and34 to concluetors 35 and 36.

Responsive to the above-mentioned operation of switching relay 25, theusual line and release relays (not shown) associated with the trunk T10are operated, and ground potential is placed on conductor 34, therebyproviding a holding circuit for the selector and for the precedingswitching apparatus after the slow-acting release relay 21 of theselector illustrated has fallen back, as will now be explained:

When line relay 20 is disconnected at the contacts of relay 25, it fallsbacl and closes a point in the circuit of vertical magnet 27 at itslower armature. Vertical magnet 27 is not operated at this -time becausethe series auxiliary relay 23 is in a. restored condition. Line relay20, at its upper armature and associated contacts open-circuits andshortcircuits the upper winding of the release relay 20, at the sametime opening the circuit through the lower windings of relays 22 and 21(relay 22 is in a restored condition at this time). It is to be notedthat series relay 22 does not operate at this time because its upperwinding has been disconnected at the upper armature of the relay. Relay21 falls baclr as soon as the circulating current in the upper windingsubsides somewhat.

Releasing lVhen the ground potential is removed from release trunkconductor 34 of trunk T10 when the connection is to be released,switching relay 25 restores and closes a circuit for release magnet 26at armature 53. By the operation ot release magnet 26 the selector isrestored to normal position, whereupon the release-magnet circuit isopened at ott'- normal contacts 17, while at oft-normal contacts 16battery potential is re-applied to conductor 11 by way of resistance 19so as to marlr the selector as available for further use.

Selecting L trunk a the next higher level It will now be assumed thatall the trunk lines accessible from the first level of bank contacts arein use when the wipers of the select r are brought to rest 'opposite thefirst level of bank contacts as hereinbefore described. Under thiscondition, there is a selector in engagement witheach ot the trunk linesaccessible from the rstlevel of bank contacts. Keeping in mind that thecontact sets and vertical test contacts are multipled togetherthroughout all ofthe selectors having access tothe trunk lines underdiscussion, it will be seen that ground potential is eX- tended bybridging wipers, such as wiper 31 of the selector illustrated, throughthe contact multiple to all of the number one contacts in the bank ofthe vertical test wipers, such as test wiper 33. Under this condition,theretore,- test wiper 33 encounters a ground potential, resulting in acircuit being closed for vertical magnet 27 through contacts of therestored series relay 22 and contacts of the still-operatedslow-restoring relay 23. This circuit includes the lower winding ofdiscriminating relay 24 andthe self-interrupting contacts of magnet 27.RelayV 24 and vertical'magnet 27 energize in series, relay 24 operatingslightly ahead of the magnet, which has a larger, heavier armature, andmust elevate the shaft. Vhen relay 24 operates, it prepares a lockingcircuit for its upper winding at its inner armature, and at its upperarmature it disconnectstest wiper 32 and connects up test wiper 31.

i When magnet 27 near the end of its stroke, and just before verticaltest wiper 38 leaves the first-level test contact and comeskintoengagement with the associated second-level contact, it interrupts itsown circuit and the circuit of relay 24, whereupon vertical magnet 27deenergizes, and again closes its interrupter contacts. The verticalmagnet can not again operate, however, because the series auxiliaryrelay 23 has a sufficiently stiff adjustmentfthat it Jfalls back anddisconnects vertical test wiper 38 before magnet 27 can operate thesecond time, even though the second-level test contact may be grounded.lt may be pointed out that discriminating relay 24 is renderedsufficiently slow-acting by the usual vcopper collar around its corethat it does not ,tall baclr while the self-interrupting contacts of thevertical magnet are open. As soon as relay 23 falls back and vertialmagnet 27'has restored its interrupter contacts, a locking circuitexists for relay 24 rae in series with vertical magnet 27, and by way ofboth windings ofrelay 24 in series. Magnet 27 does not operate in thiscircuit because of the relatively high resistance of the upper Windingof the relay.

vBy the above-described automatic vertical stepping operation the wipersof the selector have beenraised one step from their set positionopposite the iirst level to a position opposite the second level of bankcontacts. The regular rotary movement is now brought about by therotarymagnet 28 and responsive to the closure of the circuit of rotarymagnet `28 at the upper armature of the seriesauxiliary relayA 23. Sincethe discriminating relay 24 is now operated, and the test winding ofrelay 25 has been disconnected from wiper 32 andtransferred to wiper 31,the

ktesting is performed in the second level of 120 bank' section 35 inplace of in the second level of bank section 36, as is done when theWipers are brought opposite the second level of the bank contactsresponsive to the dialling of the digit 2. Assuming that the first setof contacts in the second levelfis idle (the eleventh contact set intrunk Agroup one), wiper 31 encounters a battery potential on conductor37 of the trunk T11, whereupon switching relay 25 operates with thehereinbefore described results.

It may be particularly pointed out at this time that therelease trunkconductors of trunk lines reached from the level above the onecorresponding to the digit assigned to the concerned trunk group areconnected to the bank section' 35 instead of bank section 36, therebyenabling a discriminating test to be made so that there is no danger ofthe selector seizing a trunk line in other than the dialled group.

AZZ-tf/Ywncs-busg/ condition Assuming now that all trunks are busy inthe first group when the digit 1 is dialled as hereinbefore described,the wipers are given an automatic vertical step following theiralignment opposite the iirst level of bank contacts responsive tothedigit 1. Following this additional and automatic vertical step, theWipers are rotated over the bank contacts in the second level in searchof an idle trunk. Sin-ce the remaining six trunks in group one are allin use, the hunting action of the selector continues until the wiperspass over all of the contacts in the second level, as no batterypotential is encountered by wiper 31 on any of its contacts.

When the wipers 31 to 34 pass off the last set of bank contacts in thesecond level, the overflow spring-combination, including centact sets 14and 15, are actuated. At oinormal contacts 15 the circuit of rotarymagnet 28 is interrupted, thereby terminating the rotary movement, whileat the overflow contacts 14 busy-tone current is substituted fordial-tone current, givingl the calling subscriber a characteristic busysignal to prompt him to release the partially established connection andmake the attempt later.

Completing a connection a the eccomi group Assuming now that theselector shown in the drawing is seized and prepared for operation inthe usual manner and that the calling subscriber dials the digit 2, theWipers of the selector are stepped vertically into association with thesecond level of bank contacts, following which the series relay 22 fallsback and connects up the vertical test wiper 38 in order to determinewhether or not there is an idle trunk line available in the second leveland assigned to group 2. Assumingthat there is such a trunk line,vertical magnet 27 is not operated further, as no ground potential isencountered by wiper l38; and the hunting operation takes place on thesecond level. Since discriminating relay 24 is not operated in thiscase', the testing operation is performed with wiper 32. Since the firstsix contacts in the second level of the bank of wiper 32 are notconnected to any trunk lines, the effective testing does not begin untilthe seventh contact set 'is reached. Either the seventh contact set orone of the succeeding contact sets is Jtound to the idle, and theconnection is completed in the usual manner.

From the explanation hereinbefore given, it will be understood that thewipers of the selector are automatically raised to the third level, andwiper 32 is replaced by Wiper 31 in case all of the second-group trunklines terminating in the second level are busy.

It will be understood, of course, that the manner disclosed herein forcontrolling the application of ground potential to the contacts in thevertical test bank is merely eX- emplary, and that suitablearrangements, including so-called chain relays connected to the releasetrunk conductors of the trunk lines involvedmay be used whenever foundlto be desirable.

What is claimed is:

1. In a two-motion selector switch having its bank contacts divided intoparallel rows and having a motion in one directionto 'select a contactrow and a motion in another to respond to the designation of a trunkline group by hunting 'for and extending connection to anyV idle contactset assigned group. N v

2. In combinatlon, a selector havingV its to such contact bank arrangedin parallel rows,there Lil) being a separate digit assigned to each row,groups of trunk lines corresponding to said rows, respectively, one otsaid trunk line groups occupying contacts in the row assigned theretoand additional contacts in the next adjacent Contact row, means in saidselector responsive to a digit control for bringing the selector intoassociation with the corresponding contact row, means for then causingthe selector to search over the contact row for an idle trunk line,means effective in case all trunk lines reached from such contact roware in use and in case there are additional trunk lines in the samegroup reached from the nent adjacent contact row for automaticallyTadvancing the selector to the next contact row before the trunksearching operation takes place, and means for restricting' the trunksearching action ot the selector to the trunk lines in the groupcorresponding to the digit in accordance with which the selector wasinitially positioned.

3. In combination, a. selector having bank Contact sets arrangeo ingroups, each group normally corresponding to a separate digitdesignation, the contacts in one ot said groups being divided betweentwo trunk groups bearing diiiierent digit designations, means forbringing said selector into association with said contact group as aresult of control being exercised over the selector in accordance witheither of said two digit designations, means thereupon eiiiective forstarting said selector searching over the contact sets in said groupssuccessively, and means automatically eiiiective and dependent upon thedigit in accordance with which the selector received its contro-l forpreventing the selector from making connection with any trunk line otone group and for permitting the selector to make connection with anyidle trunk line in the other group.

4. In combination, a selector having its contact bank arranged ingroups, means eliective for setting the selector' into association witha contact group by a directed movement or by a non-directed automaticmovement, the contacts of said group being divided between two separategroups ot trunk lines, and means eiiective depending' upon in which ofthe two ways the selector was brought into association with the contactgroup for predetermining with which trunk group connection will be made.

5. In combination, an automatic trunk selector having its bank contactsarranged in groups, trunk lines connected in the bank of said selectorand having different digit designations, means tor operating saidselector in accordance with the digit designation of any trunk linegroup to bring the selector into association with a group ot contacts towhich trunk lines of said group are connected, said selector having' twotest wipers, one being normally effective and the other being normallyineective, means effective when said selector is brought intoassociation with a group ot contacts and responsive to all trunk linesterminating in the said contact group corresponding into the digitsetting of the selector being in use tor automatically operatsaidselector' into association with a different one ot the contact groups,and means thereupon effective for substituting the normally ineffectivetest wiper for the normally effective one.

6. In combination, an automatic trunk hunting selector switch having itscontact bank arranged in groups, means tor directively associating thewipers ot' said selector with said group in accordance with digitdesignations, means in said selector for causing the wipers to bebrought into association with a contact group by means oi a non-directedmovement, said selector having two test wipers, and means for selectingeither of said test wipers tor use to the exclusion of the other,depending upon whether the selector is brought into association with acontact group by means of a directed movement or a nondirected movement.

7. ln combination, an automatic trunking selector having its contactbank divided into groups, directing means for setting the wipers of saidselector into association with any group by advancing the wiperssuccessively from group to group, there being one trunk group occupyingcontacts in one contact group and certain ot the contacts in the nextsucceeding Contact group, with a second trunk group occupying theremaining contacts in the last-mentioned contact group, means ettcctivewhen the selector is directively set on the iirst ot said two contactgroups for automatically giving the selector an additional non-directedmovement to the next succeeding contact group in case all of the trunklines connected to the contacts ot the first contact group are in use,means thereupon etliective for causing the selector to search for andseize any idle trunk line of the iirst group connected with the contactsot the second contact group, and means for preventing the selector fromconnecting with any one ot the trunk lines ot the second contact groupunless the selector was initiallv and directively positioned on thesecond contact group. In witness whereof, I hereunto subscribe my namethis 11th day of December, 1931.

JOHN l/VICKS.

